The invention relates to a semiconductor device for producing an electron beam, having at least one cathode comprising a semiconductor body which is provided at a major surface with an electrically insulating layer with at least one opening, in which at least one acceleration electrode is provided on the insulating layer at the edge of the opening and the semiconductor body has a pn junction within the opening.
The invention further relates to a camera tube and a display arrangement provided with such a semiconductor device.
Semiconductor devices of the kind mentioned in the opening paragraph are known from the Netherlands Patent Application Nr. 7905470 corresponding to U.S. Pat. Nos. 4,303,930 and 4,370,797.
They are used inter alia in cathode-ray tubes, in which they replace the conventional thermionic cathode, in which electron emission is produced by heating. In addition, they are used, for example, in apparatus for electron microscopy. In addition to the high energy consumption for heating, thermionic cathodes have the disadvantage that they are not immediately ready for use because they must be first heated up sufficiently before emission occurs. Moreover, in the long run the cathode material is lost due to evaporation so that these cathodes have a limited lifetime.
In order to avoid the heating source, which is troublesome in practice, and in order to also meet the other disadvantages, the use of a cold cathode has been aimed at.
The cold cathodes known from the aforementioned Netherlands Patent Application are based on the emission of electrons from the semiconductor body when a pn junction is operated in the reverse direction in such a manner that avalanche multiplication occurs. Certain electrons can then obtain such a quantity of kinetic energy as is necessary to exceed the electron work function: these electrons are then released at the surface and thus supply an electron current.
In this type of cathode, a maximum efficiency is aimed at, which can be attained by a minimum work function for the electrons. This is achieved, for example, in that a layer of material reducing the work function is applied to the surface of the cathode. Preferably, caesium is used for this purpose because this material causes a maximum reduction of the electron work function. The use of caesium also has a number of disadvantages, however. For example, caesium is very sensitive to the presence (in the environment of use of the cathode) of oxidizing gases (water vapor, oxygen). Moreover, caesium is rather volatile, which may be disadvantageous in those applications in which substrates or preparations are situated in the proximity of the cathode, as may be the case, for example, in electron lithography or electron microscopy. The evaporated caesium can then be deposited on the said objects.